Method of separating organic acids from petroleum oils by extracting the oil with an aqueous mixture of an amine and an alcohol



1956 w FIERCE ET AL 2,769,767

METHOD OF SEPARATING OR GANIC ACIDS FROM PETROLEUM] OILS BY EXTRACTING THE OIL. WITH AN AQUEOUS MIXTURE OF AN AMINE AND AN ALCOHOL Filed Julys, 1953 2 Sheets-Sheet 1 PERGENT AGlDS REMOVED BY A SINGLE EXTRACTION O 10 2O 3O 4O 5O 60 PERCENT WATER INEXTRACTING SOLVENT FIG I INVENTORS WILLIAM L. FIE/P05 BY Gil-FORD w. mose A TTORNE Y Nov. 6, 1956 Filed July 5 1953 TIME IN MINUTES REQUIRED FOR SEPARATION OF PHASES w. L. FIERCE ET AL' 2,769,757 METHOD OF SEPARATING ORGANIC ACIDS FROM PETROLEUM OILS BY EXTRACTING THE OIL WITH AN AQUEOUS MIXTURE OF AN AMINE AND AN ALCOHOL 2 Sheets-Sheet 2 FIG. 2

INVENTORS WILLIAM L. F/ERGE Gil-FORD W. CROSBY A TTOR/VE'Y METHOD OF SEPARATING ORGANIC ACI DS FROM PETROLEUM OILS BY EXTRACTING THE OIL WITH AN AQUEOUS MIXTURE OF AN AMINE AND AN ALCOHOL William L. Fierce, Algonquin, and Gifford W. Crosby, River Forest, Ill., assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio 7 Application July 3, 1953, Serial No. 365,814

10 Claims. (Cl. I96-41) This invention relates to a method of refining petroleum oils. In a more specific aspect, the present invention relates to the removal of organic acids from petroleum fractions. In a still more specific aspect, the present invention relates to the removal of naphthenic acids from petroleum fractions.

In the past, considerable work has been done in an efiort to remove organic acids from petroleum distillates in order to free the distillate of these acids and to recover the acids which find wide use as chemical intermediaries. The removal of these acids is normally brought about by contacting the petroleum distillate with an aqueous or alcoholic solution of an alkali, such as po tassium hydroxide. The alkali solution, after separation from the petroleum distillate, is then acidified to free the organic acids and the acids are then washed free with a solvent such as a low boiling distillate. However, these methods of reducing the acidity of petroleum distillates and of recovering organic acids present therein have not proved very successful due to a number of difficulties, such as the formation of emulsions during treating and the low quality of the acids recovered. The latter drawback is particularly striking in view of the short supply of naphthenic acids and the many uses which have been found for metallic naphthenates. It is well known that metallic naphthenates are superior to salts of vegetable or rosin fatty acids because of their better solubility in commercial solvents, better stability during hydrolysis, resistance to breakdown by oxidation, and resistance to breakdown by bacteria. It is also well known that various metallic naphthenates are highly desirable as ingredients for paints, as treating agents for rope, wood, etc., to prevent the growth of fungi, as agents for the resolution of stubborn oil-in-water emulsions, as components of detergents, as additives for lubricating oils, and as components of a large number of other compositions. In addition to the difiiculties pointed out above which are connected with the refining of light petroleum distillates and light lubricating oils, it is generally conceded that higher boiling organic acids which are concentrated in high boiling distillates and residual stocks are much more difficult to remove than are the lower boiling acids. For example, it is virtually impossible by following the teachings of the prior art to reduce the acidity of high boiling stocks, such as bright stock fractions. This difliculty arises from the fact that the higher boiling stocks contain high molecular weight acids, such as high molecular weight naphthenic acids. In addition to the ditficulty experienced in the removal of these high molecular weight acids, supplies of this type of acids are not generally available in commercial quantities.

It is, therefore, an object of the present invention to provide an improved method for refining petroleum fractions.

Another object of the present invention is to pro- 2,769,767 Patented Nov. 6, 195% vide an improved method for the removal of organic acids from petroleum fractions.

Still another object of the present invention is to provide an improved method for the removal of naphthenic acids from high boiling petroleum fractions.

A further object of this invention is to provide an improved treating solution suitable for use in the removal of organic acids from petroleum fractions.

Another and further object of the present invention is to provide an improved treating solution suitable for use in the extraction of naphthenic acids from high boiling petroleum fractions.

These and other objects of the present invention will be apparent from the following detailed description read in conjunction with the accompanying drawings, where- Figure l is a graphical representation of the relationship between the water content of a treating solution employed to extract naphthenic acids from a petroleum raction and the quantity of naphthenic acids removed from the oil, and

Figure 2 is a graphical representation of the relationship between the water content of a treating solution employed to extract naphthenic acids from a petroleum fraction and the time required to separate the oil phase from the treating solution phase by settling.

In accordance with the present invention, it has been found that organic acids can be removed from petroleum distillates by treating the distillate with a mixture of an aliphatic organic amine, a low boiling alcohol, and water.

The term aliphatic organic amine as employed in the present invention includes aliphatic organic amines having primary, secondary, or tertiary amine groups and aliphatic organic alkanolamines.

The term lower boiling alcohols is meant to include alcohols having a low molecular weight. These low molecular weight alcohols include aliphatic alcohols and their isomers having less than 7 carbon atoms per molecule.

The following results obtained in the extraction of organic acids from petroleum fractions illustrate the necessity of having all three components of our improved treating solution present:

Example 1.-1OO parts by weight of a deasphalted oil (having an API gravity of 21, a viscosity of 178.8 SUS at 210 F., and an acid number of 1.75) were diluted with 70.9 parts by weight of Stoddard solvent. 30 volumes of this diluted oil were subjected to a single batch extraction with 5 volumes of ethanolamine. This treatment resulted in the removal of only 5.2 percent of the naphthenic acids present in the oil.

Example 2.-30 volumes of the diluted oil employed in Example 1 were subjected to a single batch extraction with 10 volumes of a mixture of ethanolamine and water in the ratio of 1:1. This treatment failed to remove any of the acids from the oil.

Example 3.8 samples of 100 volumes each of the diluted oil employed in Example 1 were subjected to a series of batch extractions with treating solutions composed of 2.5 percent by volume of ethanolamine and i 97.5 percent by volume of a mixture of varying amounts a content of about 40 percent is reached. However, after the water content has passed 40 percent, the amount of acids removed increases much less rapidly and, as is illustrated by Example 2, if only the amine and water are employed the amount of acids extracted will drop to zero. I

Example 4.-A series of extraction similar to those of Example 3 were conducted on three samples of a 150 viscosity dewaxed bright stock. In this series of extractions, each treating solution contained 12 percent by volume of ethanolamine and the alcohol component was normal butyl alcohol. A solvent to oil ratio of 0.26 was employed in each extraction. The results of this series of extractions are shown by curve 2 of Figure 1.

A study of curve 2 will bring out substantially the same conclusions which were drawn relative to curve 1 of Figure 1. That is, substantially larger amounts of acids are removed when water is added to the treating solution than can be removed when a solution of an amine and alcohol alone is employed.

From Examples 1 through 4 and from Figure 1, it can be clearly seen that we have discovered that substantially improved results can be obtained in the extraction of organic acids from petroleum fractions if water is added to a mixture of an organic aliphatic amine and a lower boiling alcohol. However, it has also been discovered and forms a part of the present invention that the presence of large amounts of water in a solution employed in the extraction of organic acids frcm petroleum fractions causes emulsification during the extraction and makes it difficult to separate the oil from the treating solution. This discovery is illustrated by the following example:

Examole 5. samples of a 150 viscosity dewaxed bright stock were subjected to a series of batch extractions with treating solutions made up to 10 percent by volume of ethanolamine and 90 percent by volume of a mixture of varying amounts of normal butyl alcohol and water. A solvent to oil ratio of 0.4 was employed in each extraction. Following each extraction, the time required to separate the oil phase from the treating solution phase by settling was observed in each case. Figure 2 of the drawings shows the results of this series of extractions.

From Figure 2, it can be seen that the time required to separate the oil and treating solution phases by settling is about minutes for all treating solutions containing up to about percent of water. It can also be seen that the time required to separate the two phases increases at an extremely rapid rate for each incremental increase in the water content of the treating solution after 20 percent of water has been exceeded and that the time required for separation exceeds 15 hours for solutions containing 30, 40, and 60 percent of water, respectively.

Therefore, it is highly advantageous to employ treating solutions containing less than about 20 percent of water in the practice of the present invention. By employing solutions containing this preferred concentration of water it is possible to employ simple settling as a means for separating the oil phase from the treating solution phase. On the other hand, if the main requisite is the removal of large amounts of acids in a single extraction, larger amounts of water may be employedand emulsification can be reduced to a certain extent by dilution of the oil being treated with large amounts of a solvent, such as Stoddard solvent. Likewise, if large amounts of water are to be employed in order to obtain maximum acid removal in a single extraction, separation of the oil and treating solution phases can be speeded up by centrifuging or other equivalent means. In addition, Examples 6 and 7 illustrate that,

Substantially all of the acids present in an oil can. be

extracted by the treating solution as shown by actual isolation of the extracted acids from the spent treating solution. Further data indicates that three additional batch treatments of the bright stock result in the removal of a total of about percent of the naphthenic acids present in the original sample of oil.

Example 7. volumes of the broad middle cut from the vacuum distillation of a solvent extract obtained in the extraction of a lubricating oil distillate to prepare a viscosity neutral (having an API gravity of 12.7, a viscosity of 57.1 SUS at 210 F., and an acid number of 5.0) were extracted with 26.4 volumes of a treating solution composed of 11.5 percent by volume of ethanolamine, 11.5 percent by volume of water, and 77 percent by volume of isopropyl alcohol. A single batch extraction resulted in the removal of 91.2 percent of the naphthenic acids present in the oil. Further treatment of the extract oil with the same volume of fresh treating solution removed the remaining acids from the oil.

In addition to a single batch extraction or a plurality of batch extractions, it will be apparent to those skilled in the art that the various continuous contacting operations can also be employed in the practice of the present invention.

Experience in the practice of the present invention has shown that treating solutions containing about 0.1 to 40 percent by volume of an aliphatic organic amine, 2.0 to 40 percent by volume of water, and 50 to 98 percent by volume of a low boiling alcohol may be employed. For the reasons set forth above, we prefer to employ solutions containing about 10 to 15 percent by volume of an aliphatic organic amine, 10 to 20 percent by volume of water, and 65 to 80 percent by volume of a low boiling alcohol.

Aliphatic organic amines other than those set forth in the specific examples may be employed in the practice of the present invention. It is preferable that the amine employed be of such a volatility that no appreciable loss of amine occurs during the processing. Examples of amines which were found useful are dimethylamine, diethylamine, monoethanolamine, diethanolamine, hydroxyethylethylenediamine, isopropanolamine, triethanolamine, and tetraethylenepentamine.

Low boiling alcohols other than those listed in the illustrative examples include methyl alcohol, ethyl alcohol, normal propyl alcohol, isobutyl alcohol, tertiary butyl alcohol, amyl alcohol, and hexyl alcohol. The choice of an acohol for use in our improved treating solution is dependent to a certain extent upon the type of oil under-,

going treatment. For lubricating distillates, such as neutrals, any of the alcohols enumerated may be used effectively, the rapidity of separation of lubricating oil and treating solution being greatest where the lower molecular weight alcohol is used. However, for highly viscous oils, such as bright stocks, the treating solution should contain the higher molecular weight alcohols within the limitations set forth. The use of higher molecular weight alcohols with viscous oils is based on the fact that high boiling naphthenic acids are present in the viscous oils and these acids are more readily removed by solutions containing the higher boiling alcohols.

The recovery of naphthenic acids from the improved treating solutions of the present invention may be carried out by any of the known procedures heretofore used in the prior art. For example, the treating solution, after separation from the mineral oil, may be acidified with an acid, such as a mineral acid, in the presence of an added solvent, such as benzene, the amine washed from the treating solution with water, and the remainder of the solution containing the naphthenic acids neutralized and the acids recovered therefrom. A second method for the recovery of naphthenic acids from the separated treating solution would be to acidify the treating solution with carbon dioxide to form amine carbonates and free the acids, separating the freed acids from the solution, and finally heating the solution to decompose the carbonates and release carbon dioxide. Other methods of recovering naphthenic acids from the treating solution of the present invention will be apparent to those skilled in the art.

Having described and illustrated our invention, we claim:

1. The process of separating organic acids from heavy petroleum fractions comprising contacting said fraction with a mixture of to percent of an aliphatic organic amine, 10 to percent by volume of water, and to percent by volume of an alcohol having less than 7 carbon atoms per molecule.

2. The process in accordance with claim 1 in which the heavy petroleum fraction comprises a bright stock.

3. The process in accordance with claim 2 in which the bright stock is a de-asphalted residuum having an API gravity of about 21, a viscosity of about 178.8 at 210 F. and an acid number of about 1.75.

4. The process in accordance with claim 2 in which the bright stock is a viscosity de-waxed bright stock.

5. The process in accordance with claim 2 in which the bright stock is a solvent refined dewaxed bright stock having an API gravity of about 26.3, a viscosity of about 159.8 SUS at 210 F. and an acid number of about 0.38.

6. The process in accordance with claim 1 the amine is ethanolamine.

7. The process in accordance with claim 1 the amine is diethylamine.

8. The process in accordance with claim 1 the alcohol is isopropyl alcohol.

9. The process in accordance with claim 1 the alcohol is normal butyl alcohol.

10. The process in accordance with claim 1 in which the heavy petroleum fraction comprises a neutral lubricating oil having a viscosity of about SUS at 100 R, an API gravity of about 12.7 and an acid number of about 5.0.

wherein wherein wherein wherein References Cited in the file of this patent UNITED STATES PATENTS 2,059,075 Yabroff et al. Oct. 27, 1936 2,168,078 Yabroff Aug. 1, 1939 2,424,158 Fuqua et al. July 15, 1947 2,616,830 Pratt Nov. 4, 1952 

1. THE PROCESS OF SEPARATING ORGANIC ACIDS FROM HEAVY PETROLEUM FRACTIONS COMPRISING CONTACTING SAID FRACTION WITH A MIXTURE OF 10 TO 15 PERCENT OF AN ALIPHATIC ORGANIC AMINE, 10 TO 20 PERCENT BY VOLUME OF WATER, AND 65 TO 80 PERCENT BY VOLUME OF AN ALCOHOL HAVING LESS THAN 7 CARBON ATOMS PER MOLECULE. 